1. Field of the Invention
The present invention relates to a sheet folding apparatus for folding a sheet discharged from an image formation apparatus such as a copier and various types of printers, and more particularly, to a sheet folding apparatus, sheet processing apparatus, image formation apparatus and method of folding a sheet particularly for enabling compact folding to be executed.
2. Description of the Related Art
Generally, a folding apparatus is widely known where folding processing is performed, in a predetermined, on a sheet carried out of an image formation apparatus.
In addition, in recent years, such an apparatus has also been provided that the apparatus is connected to an image formation apparatus, and is disposed before a post-processing apparatus, for example, binding apparatus to perform folding processing on a sheet.
For example, Japanese Patent Gazette No. 5218836 shows a folding apparatus which is positioned between an image formation section and a post-processing apparatus and in which are disposed a transport path for guiding an image-formed sheet transported from the image formation section, three folding rollers positioned in the transport path to mutually come into press-contact, a front end stopper for regulating a sheet front end, and a folding blade for pushing the regulated sheet into among three folding rollers. Then, the folding apparatus indicates a sheet folding apparatus for repeating switchback transport of a sheet sequentially, passing the sheet through three folding rollers sequentially, and performing folding processing.
Further, Japanese Patent Gazette No. 5595009 also shows a sheet folding apparatus which is disposed before a post-processing apparatus for binding sheets, transports an image-formed sheet discharged from an image formation section once to a curved transport path, presses the sheet subjected to curve transport against three rollers mutually brought into press-contact with a deflection member, and thereby performs folding processing.
The sheet folding apparatuses shown in above-mentioned Japanese Patent Gazettes No. 5218836 and No. 5595009 require a relatively long transport path to hold a sheet length undergoing folding processing. Further, in any of the sheet folding apparatuses, the folding processing is performed by repeating operation for feeding a sheet in one direction, and carrying in three rollers, while performing switchback transport.
In addition, the folding apparatus shown in above-mentioned Japanese Patent Gazette No. 5595009 is comprised of a transport path curved above and below three rollers, is thereby made relatively smaller than the folding apparatus of Japanese Patent Gazette No. 5218836 comprised of a linear transport path, but needs a transport path over the entire length of a curved sheet.
Thus, the apparatus basically has a transport path corresponding to the sheet transport length, and further, since the folding processing is performed while switchback-transporting a sheet, requires the complicated sheet transport path with fluctuations in transport.
Particularly, in order to support the recent so-called in-body type where an apparatus for processing sheets is installed in discharge space from a reading apparatus disposed above an image formation section, miniaturization has not been attained to the extent that the apparatus is disposed in this space.